[dan0]

Better traction means that you are staying on the ground and therefore have more power and control. In other words more efficiency.

You are correct that higher pressure will roll better but with the already discussed disadvantages. Of course small knobs will roll faster but we all know what the disadvantages of that can be.

However, you are wrong about narrow tires rolling better. Again I'll link the following page from Schwalbe's Tech-Info section entitled:

Why do wide tires roll better than narrow ones?

They probably explain it better than I can. All else being equal, ( same tread pattern and same pressure ) a wider tire will roll better than a narrow one.

Ronnie.

if thats true then why are road bikes and virtually all racing tires narrow?
I also am not convinced that a 1.9" tire has the same contact patch as a 2.5" tire (@ the same pressure & circumfrence, if this is true why would anyone use a wider tire

One other point, on Schwalbes diagram they claim the contact patch area is the same , narrow tires having a longer,narrower patch vs. wide tires having a wider shorter patch, wouldnt a wider patch be better for side to side traction and a longer patch be better for acceleration / decelleration?
on a mtn bike I would rather have better side to side traction, I think a longer patch would be better for a vehicle that can actually spin the wheels

 

[Ronnie]

if thats true then why are road bikes and virtually all racing tires narrow?

Because road bikers are the ultimate weight weenies. They need/use tires that weigh in the region of 150 grams that are pumped to 145psi. so that they don't run on the rims. XC racers are not far behind. Weight is somewhat more important to them than the average mountain biker.

I also am not convinced that a 1.9" tire has the same contact patch as a 2.5" tire (@ the same pressure & circumfrence, if this is true why would anyone use a wider tire?

I know that Schwalbe and others do dyno testing on their tires. I also believe they know their stuff and if they tell me two different width tires at the same pressure have the same footprint I believe them. It's not that difficult to disprove and I could do an Internet search but I won't bother. What Earthly reason could there be for them to disseminate incorrect information on the subject? If you don't believe them prove them wrong.

One other point, on Schwalbes diagram they claim the contact patch area is the same , narrow tires having a longer,narrower patch vs. wide tires having a wider shorter patch, wouldnt a wider patch be better for side to side traction and a longer patch be better for acceleration / decelleration?
on a mtn bike I would rather have better side to side traction, I think a longer patch would be better for a vehicle that can actually spin the wheels

That is not a logical conclusion to me. The contact area is all that matters. Friction is proportional to the area making contact in all directions.

Ronnie.

 

[PCC]

if thats true then why are road bikes and virtually all racing tires narrow?
I also am not convinced that a 1.9" tire has the same contact patch as a 2.5" tire (@ the same pressure & circumfrence, if this is true why would anyone use a wider tire

One other point, on Schwalbes diagram they claim the contact patch area is the same , narrow tires having a longer,narrower patch vs. wide tires having a wider shorter patch, wouldnt a wider patch be better for side to side traction and a longer patch be better for acceleration / decelleration?
on a mtn bike I would rather have better side to side traction, I think a longer patch would be better for a vehicle that can actually spin the wheels

Road bikes run narrow tires because they are more aerodynamic and they run them at higher pressures so that they have less rolling resistance on the road. Tarmac affords the roadie much more traction than they need most of the time so this is not an issue. At the speeds that a road bike can attain these are very real benefits.

Believe it or not, given the same tire pressure (key point here) a wider or narrower tire will give you the same contact patch area for the same rider/bike weight. If you go narrower the contact patch elongates. If you go wider the contact patch gets shorter. Since the tire deforms to conform to the contour of the road surface a shorter contact patch should give less rolling resistance.

Keeping your tires on the ground gives you the ability to lay the power down over a longer period of time. This gives you more speed. The guys who race off-road in motorsports will tell you that air time is bad for elapsed times. You cannot lay down power if your tires are spinning in the air! Higher tire pressures will give you a longer coast-down distance but the last time I looked, bicycle races are not won by coasting (unless you are a downhill racer, I guess).

 

[dan0]

Road bikes run narrow tires because they are more aerodynamic and they run them at higher pressures so that they have less rolling resistance on the road. Tarmac affords the roadie much more traction than they need most of the time so this is not an issue. At the speeds that a road bike can attain these are very real benefits.

Believe it or not, given the same tire pressure (key point here) a wider or narrower tire will give you the same contact patch area for the same rider/bike weight. If you go narrower the contact patch elongates. If you go wider the contact patch gets shorter. Since the tire deforms to conform to the contour of the road surface a shorter contact patch should give less rolling resistance.

Keeping your tires on the ground gives you the ability to lay the power down over a longer period of time. This gives you more speed. The guys who race off-road in motorsports will tell you that air time is bad for elapsed times. You cannot lay down power if your tires are spinning in the air! Higher tire pressures will give you a longer coast-down distance but the last time I looked, bicycle races are not won by coasting (unless you are a downhill racer, I guess).

so you and schwalbe contend that a 26" x1" wide tire @ 30lbs has the same contact area as a 26" x2.6"? how about 26"x6" or 26" x 10"
I would think there would be a range where this is & isnt possible

 

[Ronnie]

so you and schwalbe contend that a 26" x1" wide tire @ 30lbs has the same contact area as a 26" x2.6"? how about 26"x6" or 26" x 10"
I would think there would be a range where this is & isnt possible

You've got to be reasonable. The assumption is that it is possible to ride the tire at the same pressure. A 1" wide tire ( about the same as a road bike tire ) at 30psi. will distort so much you will be riding on the rim. And yes, a 2.6" tire with the same construction as a 2.0" tire will have the same footprint area at 30psi.

Ronnie.

 

[Slobberdoggy]

And what about the claim that the friction between tubes and tires (at MTB pressures, under deformation) burns watts?

I haven't tried tubeless yet, but have seen numerous claims and studies -- usually posted in the weight weenies forum -- showing that tubed tires generally take an increased amount of energy to turn, often attributed to this tube rub phenomenon.

ANSWER

 

[PCC]

so you and schwalbe contend that a 26" x1" wide tire @ 30lbs has the same contact area as a 26" x2.6"? how about 26"x6" or 26" x 10"
I would think there would be a range where this is & isnt possible

Maybe at the extremes but my understanding of how this works is that the contact patch area remains the same if you keep the air pressure the same.

Car tires undergo this phenomenon. Because you are switching to low-profile but wider tires on your car doesn't mean that you are increasing the contact area between the tire and the ground, you are only making it wider but less long.

 

[Rod]

Schwalbe has missed an important factor with this experiment. If the area of contact is the same it would take more watts to power the wider tire because it is simply heavier. Therefore the advantages gained having less rolling resistance will be lost.

 

[dan0]

Maybe at the extremes but my understanding of how this works is that the contact patch area remains the same if you keep the air pressure the same.

Car tires undergo this phenomenon. Because you are switching to low-profile but wider tires on your car doesn't mean that you are increasing the contact area between the tire and the ground, you are only making it wider but less long.

what difference does it make if you cant realistically run the same exact tire at the same pressure & different widths
if the contact patch is the same then why have wide tires? for the extra weight?
I notice whenever cars race the tires are much wider than on standard everyday cars, whats the advantage to the wider tires? they are heavier and run hotter,
maybe , theoretically, in a lab you can make the patches the same but in the real world the wider tires are manufactured differently than narrow and I still say my 2.5 weirwolves are slower and grip better than the 2.S and its because there is more rubber on the trail at the same pressure

 

[Rod]

Dan is definitely onto something about the air pressures. If you also look at Schwalbe they recommend different air pressures depending on the width of the tire so their experiment is completely pointless. If they used their recommended air pressure chart that I pasted below and then compared the rolling resistance of the two tires, wattage needed to achieve a certain speed, grippage, and acceleration it would be an amazing experiement that I would love to read about.

Straight from the Schwalbe website that has a link posted earlier in this thread

"Tire section
width Recommended
inflation pressure
20 mm 7,5-9,0 bar
23 mm 7,5-8,0 bar
25 mm 7,0 bar
28 mm 6,0 bar
30 mm 5,5 bar
32 mm 5,0 bar
35 mm 4,5 bar
37 mm 4,5 bar
40 mm 4,0 bar
42 mm 4,0 bar
44 mm 3,5 bar
47 mm 3,5 bar
50 mm 3,0 bar
54 mm 2,5 bar
57 mm 2,2 bar
60 mm 2,0 bar"

what difference does it make if you cant realistically run the same exact tire at the same pressure & different widths
if the contact patch is the same then why have wide tires? for the extra weight?
I notice whenever cars race the tires are much wider than on standard everyday cars, whats the advantage to the wider tires? they are heavier and run hotter,
maybe , theoretically, in a lab you can make the patches the same but in the real world the wider tires are manufactured differently than narrow and I still say my 2.5 weirwolves are slower and grip better than the 2.S and its because there is more rubber on the trail at the same pressure

 

[Ronnie]

Dan is definitely onto something about the air pressures. If you also look at Schwalbe they recommend different air pressures depending on the width of the tire so their experiment is completely pointless. If they used their recommended air pressure chart that I pasted below and then compared the rolling resistance of the two tires, wattage needed to achieve a certain speed, grippage, and acceleration it would be an amazing experiement that I would love to read about.

What are you going on about? If you are the average Joe in Europe who uses a bike for utility, you go into a bike shop ( or supermarket ) to buy a tire, you look up the recommended pressure to use in it. On the other hand, I have two Continental tires, one is 2.1. and the other 2.3. They both have a pressure range of 35 to 65psi. molded onto the casing and I'll play around with the pressure to find what I like. It is a simple statement of fact that if I pump them both to the same pressure the larger tire has less rolling resistance. Schwalbe didn't invent the statement as a sales gimmick. The following is from a Wikipedia reference entitled Rolling Resistance. ( I'm sure there are many other references too. ) Under Factors that contribute it states:

"Dimensions - rolling resistance is related to the flex of sidewalls and the contact area of the tire. For example, at the same pressure wider bicycle tires have less flex in sidewalls and thus lower rolling resistance (although higher air resistance)."

There are other factors listed like:

"Sidewall deflection is not a direct measurement of rolling friction. A high quality tire with a high quality (and supple) casing will allow for more flex per energy loss than a cheap tire with a stiff sidewall. Again, on a bicycle, a quality tire with a supple casing will still roll easier than a cheap tire with a stiff casing. Similarly, as noted by Goodyear truck tires, a tire with a "fuel saving" casing will benefit the fuel economy through many casing lives (i.e. retreading), while a tire with a "fuel saving" tread design will only benefit until the tread wears down."

Discussing low profile racing car tires in conjunction with the tires on your SUV is pointless. They are designed for different purposes and are constructed differently. The arguement is intended to compare apples with apples. If I compare a Little Albert with a Fat Albert at say 30psi., the Fat Albert has less rolling resistance. I don't think Schwalbe care which you buy. They probably cost about the same but the Fat Albert may not fit in your frame/fork.

Ronnie.

 

[PCC]

what difference does it make if you cant realistically run the same exact tire at the same pressure & different widths
if the contact patch is the same then why have wide tires? for the extra weight?
I notice whenever cars race the tires are much wider than on standard everyday cars, whats the advantage to the wider tires? they are heavier and run hotter,
maybe , theoretically, in a lab you can make the patches the same but in the real world the wider tires are manufactured differently than narrow and I still say my 2.5 weirwolves are slower and grip better than the 2.S and its because there is more rubber on the trail at the same pressure

I thought about it some more and I believe it to be something like this: the air pressure inside the tire can support a certain amount of weight per PSI of tire pressure. The tire casing will deform until it reaches a point where enough surface area is making contact with the ground to support the weight of the bike and rider. This also means that if you increase the tire pressure the contact patch shrinks and if you decrease the tire pressure the contact patch increases. So, if you are not changing the tire pressure inside the tire but changing the tire size the amount of pressure inside the tire remains the same to hold up the weight of the rider and bike so the contact patch will remain the same regardless of the size of the tire.

Wider mountain bike tires, because they are wider, allow you to run a lower tire pressure than you would if you run a narrower tire. This is because the wider tire increases the contact area available so you now can run less pressure to increase traction (tire conforms to road irregularities better) with less worry about pinch flats.

Cars run wider tires for sporting purposes because you can get much more sideways loading on even your garden variety economy car than your average car can put into forward motion. Look at dragsters. They run tall, narrow tires in the rear under low pressures. This gives them a long, narrow contact patch for the best traction possible for acceleration because they have much more enging power than traction and they are trying to get as much traction for forward motion as possible. Road racers don't win races by all-out forward acceleration, for the most part, but by being able to corner hard. That's why they run wide tires on race cars. Mind you, they don't run rediculously wide tires on race cars because they also need to accelerate out of turns and brake hard going into it. Sports cars on the road go with wide tires more as a fad than anything else.

http://auto.howstuffworks.com/question506.htm To answer the question about how 30 PSI in your car tires holds up the weight of your two ton car, HowStuffWorks.com explains:

For your 2-ton (4,000 lb) car, you will find that the area of the contact patch is about equal to the weight of the car divided by the tire pressure. In this case 4,000 pounds divided by 30 pounds per square inch equals 133 square inches. That may seem like a lot, but your car's tires are probably about 7 inches wide. That means that the contact patch for each tire will be about 4.75 inches long.

Notice that tire width doesn't factor in to the equation other than as a way to give you the measurements of the contact patch itself.

 

[Rod]

Ronnie I'm not trying to argue with any of the statements you have made this far, but I see problems with their experiment. A wider tire does have less rolling resistance, but it weighs more. Everyone can agree on this and it would take more energy, watts, to get the heavier tire to the same speed as the narrow tire. Therefore, I believe the less rolling resistance that the larger tire has will be canceled out by the increase in weight. The last part of my post is about how people run difference tires at different PSI. Someone will not run a large tire and a skinny tire at the same PSI and multiple posters have stated this. I also believe that should have been a factor in their experiment.

 

[Ronnie]

Ronnie I'm not trying to argue with any of the statements you have made this far, but I see problems with their experiment. A wider tire does have less rolling resistance, but it weighs more. Everyone can agree on this and it would take more energy, watts, to get the heavier tire to the same speed as the narrow tire. Therefore, I believe the less rolling resistance that the larger tire has will be canceled out by the increase in weight. The last part of my post is about how people run difference tires at different PSI. Someone will not run a large tire and a skinny tire at the same PSI and multiple posters have stated this. I also believe that should have been a factor in their experiment.

To use the example of Little Albert and Fat Albert above, We are talking about ±200g. I spend a very little time of my ride accelerating it but I do spend most of my ride fighting against rolling resistance. Especially when it counts most, going up hill. It could also be argued that once I have accelerated the heavier tire it behaves like a flywheel and helps me keep the momentum.

I've spent most of my adult life as an airline pilot and have been conditioned to comply with limitations. If the minimum pressure on both tires is the same that is where I'll run them, at least I'll try it to see how it feels.

Ronnie.

 

[Ronnie]

I thought about it some more and I believe it to be something like this: the air pressure inside the tire can support a certain amount of weight per PSI of tire pressure. The tire casing will deform until it reaches a point where enough surface area is making contact with the ground to support the weight of the bike and rider. This also means that if you increase the tire pressure the contact patch shrinks and if you decrease the tire pressure the contact patch increases. So, if you are not changing the tire pressure inside the tire but changing the tire size the amount of pressure inside the tire remains the same to hold up the weight of the rider and bike so the contact patch will remain the same regardless of the size of the tire.

Wider mountain bike tires, because they are wider, allow you to run a lower tire pressure than you would if you run a narrower tire. This is because the wider tire increases the contact area available so you now can run less pressure to increase traction (tire conforms to road irregularities better) with less worry about pinch flats.

Cars run wider tires for sporting purposes because you can get much more sideways loading on even your garden variety economy car than your average car can put into forward motion. Look at dragsters. They run tall, narrow tires in the rear under low pressures. This gives them a long, narrow contact patch for the best traction possible for acceleration because they have much more enging power than traction and they are trying to get as much traction for forward motion as possible. Road racers don't win races by all-out forward acceleration, for the most part, but by being able to corner hard. That's why they run wide tires on race cars. Mind you, they don't run rediculously wide tires on race cars because they also need to accelerate out of turns and brake hard going into it. Sports cars on the road go with wide tires more as a fad than anything else.

http://auto.howstuffworks.com/question506.htm To answer the question about how 30 PSI in your car tires holds up the weight of your two ton car, HowStuffWorks.com explains:

Notice that tire width doesn't factor in to the equation other than as a way to give you the measurements of the contact patch itself.

PCC, very well researched and put. Makes perfect sense. So with my 220lb. carcass and approximately 30lb. bike, if I put 30psi. in my tires my contact patch is approximately 8.3 in.² or 4.15in.² per tire, irrespective of tire size. Actually probably not a 50/50 split as weight is not distributed equally.

Ronnie.

 

[Rod]

I agree with your statements about how the larger tire should keep the momentum easier once accelerated, but I still believe Schwalbe's experiement has inconclusive evidence. Schwalbe's experiements seem to be in their first stages and like I said earlier I'm waiting for a very thorough experiment to come from this company. They are on the right track and I'm not arguing about any of their information, but there are more factors to consider.

 

[LMN]

As mentioned earlier rolling resistence depends on many things.

Take two tires identical tires converted to one to tubeless and leave the other with a tube. At equal air pressures the tubeless tire will roll faster on all terrain. This is due to the friction of a tube inside the tires.

Now the main advantage of tubelss is you can run less air pressure and not flat. Now dropping air pressure will reduce rolling resistence in some situations, depending on how low you go. Low pressure will make you bike roll quicker in rough terrain but on smooth terrain (pavement) it will be slower.

Air pressure is the hardest thing to get right on a bike. Too much your bike handles terrible, too little you flat and the bike is slow on smooth ground.

 

[ralph029]

Next question

I have to say, I really enjoyed this thread! Oodles of great info and opinions! Thank you. Now I pose a second question that probably has an easy answer. I have decided to race tubeless this year as a result of this thread. I am waiting for Bontrager to send me the rim strips to go along with my Race Disc 29's and my Dry X tires. I have dropped my pressure to 28 lbs, both front and rear. I am 155 lbs. I have my Reba Race set to 100 psi. Will the wheels/tires roll differently without tubes as they do with the tubes currently, all other things being the same? Thanks

 

[Ronnie]

Logic dictates that the rolling resistance will be greater with the tubes inserted. There is more material being flexed and using energy, provided the pressure is the same. Why don't you try it both ways and let us know.

There was this thread in the weight weenies thread a short while ago on this subject which was quite interesting.

Ronnie.

 

[ewarnerusa]

I think the answer to the OP is that the tubeless setup reduces the rotational mass of the tires, reducing inertia and therefore requiring less force to accelerate. There is also the concept that the tube encounters friction against the inner sidewalls of the tire as the tire deforms. This friction robs some of the energy from the forward motion. This has been noted by Derby, Slobberdoggy and Speedub.Nate in this thread.

I'm no physicist either, but I do have an engineering degree. My opinions on some notions in this thread:

Lower pressures allow for better traction. But it my mind, the increased traction/friction while pedaling makes the tire faster, not slower. With the tire "gripping" the ground better, more energy is transferred into forward motion rather than being wasted by slipping. I can visualize this friction causing increased drag during coasting or braking conditions, but if power is being put to the pedals then better traction equals faster.

The Schwalbe thing... I get what Schwalbe is saying and I buy it. The caveat with Schwalbe's claim is that the narrow and fat tires are at the same pressure and therefore have the same deflection area. Useful if contemplating using the 1.95" or the 2.3" MTB tire in a muddy XC race where you'll be airing down, but not accurate for claiming that a skinny road tire doesn't roll as well as a fat tire because the higher pressure of the road tire is not taken into account. I guarantee that pressure will affect the "Distance S" in the Schwalbe diagram and "make the tire round so it rolls better."